Plastic conduit and fittings are currently used extensively and they have, in many instances, replaced cast iron or copper conduit and fittings. A technique used for coupling the plastic conduit has been to brush a suitable solvent on one end of the conduit and then slip the conduit into a desired fitting. The problem with the solvent coupling technique is that the solvent must be brushed on and then after the coupling, a certain set-up or dry time is required until a proper seal is made.
Slip-in coupling assemblies have been used as an alternative to the solvent technique. In the use of a slip-in coupling, a conduit is inserted into the coupling assembly and an interference fit is caused between the outer diameter of the conduit and a flexible seal that forms part of the coupling assembly. One of the problems that has existed with the slip-in coupling is that too much force is required to push the conduit into the coupling assembly and form the interference fit. The installer normally must lubricate the seal and manipulate the conduit until it finally slips into the coupling. These prior assemblies have caused the installers to spend excessive amounts of time and effort in making the connection between the conduit and coupling assembly.
Another problem exists when the plastic conduit is buried under ground as a drain or a sewer line. The ASTM requires that the slip-in coupling seal against 10 psi exterior pressure to prevent infiltration of fluid from the outside. It has been difficult to maintain ease of installation and achieve the required testing prescribed by ASTM.
Thus, the present invention relates to a conduit coupling assembly including a flexible elastomeric seal for fastening a conduit to the coupling and for sealing the coupling against interior leaking or exterior infiltration.